oakley



July 18, 1939. H. D. OAKLEY INDUCTOR COMPASS 2 Sheets-Sheet 1 OriginalFiled June 12, 1936 July 18, 1939. H. D. OAKLEY INDUCTOR COMPASS 2Sheets-Sheet 2 i ry .D- OaFZey M 1 a? Q Original Filed June 12, 1936Reissuecl July 18, 1939 UNITED STATES INDUCTOR COMPASS Henry D. Oakley,Woodlynne, N. J.

Original No. 2,132,183, dated October 4, 1938, Se-

rial No. 84,956, June 12, 1936.

Application for reissue April 13, 1939, Serial No. 267,729

9- Claims.

The present invention relates to devices for indicating angles, such forexample as earth inductor compasses, which indicate the horizontal anglebetween a given reference line and the horizontal component ofthevearths magnetic field.

The present invention is useful in connection with such compasses, andis described as embodied in an instrument of this type, but it will beunderstood that the invention has many other uses, and is not in any waylimited to compasses or other like instruments.

Broadly, the present invention relates to means for developing twoalternating electromotive forces of identical frequency but differing inphase according to the direction of the magnetic field employed ingenerating one of said forces. Such electromotive forces arethenemployed, in a well known manner, for energizing a phase indicator,which shows the phase angle between the two generated voltages. When theearths magnetic field is used in generating one of said voltages, saidother voltage being generated by means not in any way responsive to saidfield, the phase indicator will in fact serve as a compass. The sameapparatus, however, may be used to indicate the angle between anypredetermined reference line and any desired magnetic field, as will beobvious from the description which follows:

It is a general object of the invention to provide means for generatingtwo alternating voltages of identical frequency, which means shall besmall, light in weight, compact, and inexpensive. Another object is theprovision. of such means, one of said voltages being generated withoutthe use of any natural or artificial magnetic field, whereby the phaserelation of the two volt-- ages does not depend upon the direction ofthe earths field or any other magnetic field.

More specifically, it is an object of the present invention to provide arotor having a coil adapted to be rotated in a magnetic field, and acondenser plate adapted to be rotated past a fixed condenser plate, andmeans for driving said rod tor, thereby setting up two alternatingvoltages of identical frequency but differing in phase according to thedirection of said magnetic field. A further object is the provision of anovel, compact, inexpensive and advantageous earth inductor compass.

Other and further objects, features, and advantages will be apparentfrom the description which follows taken in connection with theaccompanying drawings in which:

Figure l is a diagrammatic showing of the general arrangement of thethree essential parts;

Figure 2 is a View partly in section of the casing of an indicator, thecoils and gearing being shown in side elevation;

Figure 3 is a sectional view through the interior of the indicator withthe casing removed; Figure 4 is a plan view of the indicator;

Figure 5 is a side elevation of a vertically disposed inductor unit;

Figure 6 is a vertical sectional view through the inductor unit on theline 6-6 of Figure 5;

Figure '7 is a sectional view on the line 'l--l Figure 5;

Figure 8 is a sectional view on the line 88 of Figure 5;

Figure 9 is a diagrammatic circuit view of the inductor units;

Figure 10 is a diagram showing the connections between the inductor unitand the indicator, including the amplifier circuit;

Figure 11 is a diagrammatic View showing the circuit connections of amodified form of indicator;

Figure 12 is a diagrammatic view showing the circuit connections of anelectrostatic form of indicator; and

Figure 13 is a view in perspective of a magnet and pole piece indetached relation.

In order to facilitate an understanding of the invention, reference ismade to the embodiment thereof shown in the accompanying drawings anddetailed descriptive language is employed. It will nevertheless beunderstood that no limitation of the invention is thereby intended andthat varions changes and alterations are contemplated such as wouldordinarily occur to one skilled in the art to which the inventionrelates.

In carrying out my invention I provide a simple inductor for generatingan alternating voltage resulting from the relative motion of a coil withrespect to the horizontal component of the earths magnetic field andalso to set up another alternating voltage resulting from the varyingcapacitance between a fixed and a moving electrode.

Referring particularly to Figures 5 to 9, inclusive, of the drawings Ihave shown therein an inductor unit including a coil i of moderate turnsof fine wire which is mounted in a groove in a cylinder 2 made ofinsulating material. The

latter has stub shafts 2 for rot'atably mounting =15 the cylinder andthe coil on a vertical axis. At the lower end of the cylinder there is abucket wheel 3 which is rotated by air jets emerging from nozzles 4 as aresult of pressure diiference, or by other suitable means (not shown). Asemicircular plate or electrode 5, which may be a thin piece of aluminumfoil, is secured to the surface of the cylinder 2 to revolve therewith.

A fixed plate or electrode 6 of semi-cylindrical shape is disposedadjacent to and concentric with the electrode 5 as shown in thedrawings. In actual use in a compass, the inductor unit just describedwill be mounted in gimbals or controlled gyroscopically or by anysuitable means (not shown) so that the axis of the rotor will bemaintained in a vertical position.

The construction just described forms a simple inductor for generatingtwo alternating voltages of the same frequency. One voltage is set up bythe rotation of a coil in a magnetic field, in this case the horizontalcomponent of the earths magnetic field. The. other voltage is set up bythe varying capacitance between the fixed and the moving plates 5 and B.

The indicator is illustrated in Figures 2 to 4. It consists of anexterior casing I which bears a circular glass plate 8 beneath which isa compass card 9.

At III (Fig. 4) I have indicated a lubbers line formed on the undersideof the glass plate 8, and at H, a steering and course indicator. Securedto the casing I is a base I2 upon which is mounted a bearing ring I3.Carried by the bearing ring are four pole pieces M. An upper pole pieceI5 is connected by the field cores I6 to the lower pole pieces l4 andcoils H and II are provided as shown in the drawings. A gear IB ismounted on the upper pole piece I5 and the compass card 9 is mounted onthe gear, as shown, to turn therewith. A coil I9 is disposed between thepole pieces as shown, and this coil is secured to the pivot shaft of theneedle I I so that the latter is turned with the coil. The coil I9 is inthe field of the magnetic flux set up by current flowing through coilsI'I and I I as will be hereinafter explained. A collar is threaded intothe base I2 and forms a guide for the bearing ring I3. This collar isheld in position by means of a nut 2|. A knob 22 is provided with ashaft 23 centrally disposed in a guide 24 carried by the casing I. Theshaft bears a pinion 25 meshing with the gear I 8. A plate 26 having athrust bearing 21 supports the pivot shaft I I In Figure 10 I have shownthe circuits by means of which the device is operated. In this figure Aindicates in general the amplifier input circuit. This includes theinductor coil I associated with a grid 28, and the electrode plates 5and 6 associated with a grid 29. B indicates in general the outputcircuit including the plates and 3| of the output tubes. Phase splittingand phase control circuits for the electromagnetic type of indicator areshown in general at C and the indicator circuits at D.

Two alternating voltages are set up in the following manner in Figure10. The rotating coil I is connected between the grid 28 and the ground.The rotating plate 5 is connected to the ground and the fixed plate 6 isconnected through a blocking condenser to grid 29. Grids 28 and 29 arebiased sufliciently negative so that at no time is there grid currentflowing. A fairly high D. C. voltage is maintained between +3 and theground. This potential acting through the high resistance 39 holds asubstantially constant charge on plate 6. When the rotor of the inductorunit spins an alternating voltage is set up across grid 28 and theground due to the action of the earths magnetic field upon coil I. Atthe same time plate 5 is also revolved, and so the capacitance betweenplates 5 and 6 is fluctuating. Since the charge on plate 6 remainsconstant and the voltage across 5 and 6 must fluctuate this gives riseto an alternating voltage between grid 29 and the ground. Obviouslythese two voltages must be of the same frequency since coil I and plate5 are mechanically tied together and rotated as a unit with no relativemotion between them. Since plate 6 never changes its position withrespect to the ship that is carrying the compass and since the ship doeschange its position with respect to the earths magnetic field, it isevident that the phase angle between the two alternating voltages canhave any Value between 0 and 360 degrees.

In the system described thus far there is practically a zero currentflow, that is, it is a potential operated system. This means that ifresistance variations are introduced into the circuits as the stubshafts 2 rotate in their bearings noobjectionable effects will be set upin the system.

This arrangement then provides a means for generating two alternatingvoltages of the same frequency and whose phase angle is controlled.- bythe direction in which the system is pointing with respect to thedirection of the earths magnetic field or such other field as may beused.

In carrying out the invention use is made of the forces set up by arotating field acting upon a simple alternating one.

In Figure 10 two sets of coils I'I and II are shown. These are the fieldcoils of the indicator and are located physically 90 degrees apart. Thecircuit consisting of the condenser 44, the resistor II and the coil l1obtains. its energy from the same amplifier as does the circuitconsisting of the coil 43 and resistor 42 and the coil I'I electricalvalues of the elements of these two circuits are so chosen that thephase angle between the current flowing in coil I! and that flowing incoil I I is 90 degrees. The magnetic flux set up by these two currentsin the field structure of the indicator then has the well known rotatingcharacteristic. Coil I9 is situated in this field and is mounted on ashaft so that it is free to rotate, and this coil is supplied withcurrent from the other amplifier. This current sets up about coil I9 asimple alternating magnetic field. Since the frequency of the rotatingand the alternating fields is the same, the forces set up by the actionof the two fields are such that coil I9 assumes a position of rest andthis position is determined by the phase angle of the two amplifieroutput voltages.

The circuit elements 45, 45, 41 and 48 provide compensation to preventindicator errors which would ordinarily appear whenever the speed of theinductor rotor deviated from some pre-assigned value.

The device, as pointed out above, consists essentially of three units,the inductor unit shown generally at Iin Figure 1 the amplifier unit atII, and the indicator unit at III. Between the inductor unit I and theamplifier unit II are two Wires 32 and 33 enclosed in a shell 34 whichcan be metal tubing or metal braid and forms the ground return of thecircuits. Between the amplifier unit and the indicator unit there arethree wires indicated at 35, 35 and 37, respectively, enclosed in ashell 38. It will be noted that there are absolutely no mechanicalconnections between these three units.

From the foregoing description of the various parts of the device theoperation thereof may be readily understood. The circuit illustrated inFigure 10 is for the electromagnetic type, as stated.

Assuming that the rotor has been set in operation, the coil I rotatingin the earths field impresses a sine wave of voltage across the grid 28,the battery +B acting through 39 charges the fixed electrode 5. Aselectrode 5 rotates the capacitance of 6 to ground varies and so thevoltage across 6 and ground varies. Hence the voltage impressed acrossgrid 29 varies in the same way. The electrode plates 5 and 6 are soshaped that the voltage wave impressed on the grid 29 is sinusoidal.Thus there are two sine voltages generated. Since the coil and themovable electrode 5 are mechanically connected together and turn aboutthe same axis there can be no frequency difference between the twovoltages but since the stationary electrode never changes its positionwith respect to the moving body to which it is attached, and since thecourse of the moving body does change with respect to the direction ofthe earths field, the phase between the two generated voltages willchange and in direct proportion to the course changes.

These two induced voltages are amplified and are impressed on theindicator in the manner shown in the drawings. It will be observed thatthe coil I9 carries alternating current whose frequency is the same asthat of the indicator field. During one revolution of the indicatorfield the coil I9 is subjected to a sinusoidally varying torque thatreverses its direction four times. Because of its inertia the coilcannot follow these torque reversals but takes up a stable position ofrest. This position is at the point where the current in the coil is amaximum. The point where maximum current occurs is determined by thephase angle of the two induced voltages in the inductor unit. Thereforethe coil takes up a position which is controlled by the heading of themoving body with respect to the horizontal component of the earthsmagnetic field. By providing the movable coil with a needle or pointer,such as that shown at II, that travels over a 360 scale, shown at 9, thedevice becomes a compass.

It will be noted that in the device described above the output tube ofone amplifier feeds into a phase splitting circuit. This circuitsupplies two currents that differ in phase by 90. To secure a 90 phasedisplacement between the two field currents. the resistances of 4| and42 must be equal, and also the square root of the ratio of the reactanceof 43 to that of 44 must be equal to the resistance of 4|. Therefore tohave proper phase control of the current flowing through the moving coilI9, 45 must equal 4!, 46 must equal 42, 41 must equal 43 and 48 mustequal 44. The indicator derives its rotating field from these twocurrents. The other output tube feeds into a phase control circuit fromwhich is obtained a current for moving the coil IQ of the indicator. Thereason for using this phase control circuit is to prevent indicatorerrors which would ordinarily appear whenever the speed of the inductorrotor departed from a pre-assigned value.

In Figure 11 I have shown a circuit in which a low impedance metal ringor properly shaped iron vane 40 is. employed moving in a field which isthe resultant of two equal but oppositely rotating fields, and carriesthe compass needle. In this form there is no external moving coilcircuit.

The double field magnetic type indicator with a single turn coil (metalring) is the simplest, most rugged, and cheapest to build. This form ofindicator is also advantageous in that the bearings of the moving partsmay be designed solely for supporting the moving system with a minimumof friction, there being no necessity of providing electrical connectionthrough the bearings, and the iron magnetic circuit of the indicator canbe arranged in a very compact manner.

The substitution of the electrostatic for electromagnetic effects willproduce the same result.

In Figure 12 I have shown the circuits for the electrostatic indicator.Condenser 49 and resistance 50 are placed in the phase splitting circuitwhile resistance 5| and condenser 52 are in the phase control circuit.53 and 54 are the field plates and 55, shown partly in dotted lines, isthe moving vane. For proper action the reactance 49 should beapproximately equal to the resistance 50 and 5| and 52 should havecorresponding values.

Advantages of the electrostatic type of indicator are that it can beused to measure the phase angle between fairly high frequencies, atwhich high frequencies the magnetic type indicators of Figures and 11may be unsuitable for obvious reasons. Also, there need be only oneelectrical connection through the bearing for the moving system, and thecurrent carried by this connection is exceedingly small.

In the electrostatic type the parts are of smaller physical size andweight and smaller power output is required from the amplifiers tooperate the indicator. However, it is not so apt to withstand shocks andvibration to which it will be subject in service and more skill isrequired in building it. In addition the insulation of all the circuitsmust be maintained at a high value.

In using either type of this device the navigator rotates the gear I8 bymeans of the knob 22, thus rotating the field coils ll and 11 and thechart, so that any point on the scale can be made to coincide with thelubbers line. This enables the navigator to set the compass so that thecompass course to be followed lies on the lubbers line. The pilot thensimply steers the course so that the needle of the compass aligns withthe lubbers line, thus making of this instrument both a compass and acourse indicator.

The device has numerous advantages. The mechanical drive between theinductor unit and the instrument board is eliminated. There are nobrushes, commutators, or slip rings. There are but two moving parts, theinductor rotor and the indicator moving coil. There are no delicateparts requiring precision adjustments for proper operation of thecompass.

The actual compass course of a moving body is shown, and not merelywhether the body is moving along a previously determined course.

Compass readings are not affected by variation in the strength of theearths field nor are they affected by contact resistances, speed of theinduction rotor, or by amplifier gain whether due to changes in supplyvoltages or aging of the tubes.

Having thus described the invention. what is claimed as new and desiredto be secured by Letters Patent is:

1. In an inductor compass, an indicator unit having a plurality of fieldcoils provided with pole pieces, a rotatable coil centrally disposedbetween said pole pieces electromagnetically reacting with andcontrolled by the field set up by the coils, a needle carried by saidcoil, a direction chart, a stationary lubbers line, means for rotatingsaid field coils, pole pieces, and chart simultaneously to bring saidchart into registration with said lubbers line, and means for producinga rotating field in said field coils, said means comprising an inductorunit for generating an alternating voltage from the horizontal componentof the earths magnetic field, and a second means for generating analternating voltage of the same frequency, an amplifying means for eachvoltage, one of said amplifiers being associated with certain of saidfield coils for energizing them and the other of said amplifiers beingassociated with other field coils, said rotatable coil and needleadapted to assume a position of rest, the position being determined bythe phase angle of the output voltages of the amplifying means.

2. In an inductor compass, an indicator unit having a plurality of fieldcoils, a rotatable coil electromagnetically reacting with and controlledby the field set up by the coils, a needle carried by said rotatablecoil, a chart disposed beneath the needle, means for simultaneouslyrotating the chart and field coils, a stationary lubbers line, means forproducing a rotating field in said field coils, said means comprising aninductor unit for generating an alternating voltage from the horizontalcomponent of the earths magnetic field and a second means for generatingan alternating voltage of the same frequency. an amplifying means foreach voltage. a split phase circuit associated with one of saidamplifying means and having connections with certain of the field coilsand a phase control circuit assoc ated with the other amplifying meansand being connected with the rotatable coil, said rotatable coil andneedle adapted to assume a position at rest, the position beingdetermined by the phase angle of the output voltages of the amplifyingmeans.

3. In a device for indicating the angular relation of a magnetic fieldwith respect to a given reference line. a rotatable coil disposed insaid magnetic field, a condenser plate rotatable with said coil, meansfor synchronously rotating said coil and condenser plate, a secondcondenser plate mounted adjacent to the orbit of said first condenserplate and fixed in relation tosaid reference line, means for keepingsaid condenser charged, a phase indicating device, and means connectingsaid indicating device to said rotatable coil and said condenser, saidrotatable coil and said condenser being adapted to generate alternatingpotentials whose phase relation is dependent upon the direction of saidmagnetic field with respect to said reference line. whereby saidindicating device is caused to re ister the angular relation of saidmagnetic field to said reference line.

4. In a device for indicating the angular relation of a magnetic fieldwith respect to a given reference line, a rotor disposed in saidmagnetic field and carrying a coil and a condenser plate. means fordriving said rotor, a fixed condenser plate mounted adjacent the orbitof said first condenser plate, said condenser plate constituting avariable condenser, means for keeping said condenser charged, a phaseindicating device, and means connecting said indicating device to saidrotatable coil and said condenser, said rotatable coil and saidcondenser being adapted to generate alternating potentials whose phaserelation is dependent upon the direction of said magnetic field withrespect to said reference line. whereby said indicating device is causedto register the angular relation of said magnetic field to saidreference line.

5. In a device for indicating the angular relation of a magnetic fieldwith respect to a given reference line, a rotor disposed in saidmagnetic field and carrying a coil and a condenser plate, means fordriving said rotor, a fixed condenser plate mounted adjacent the orbitof said first condenser plate, said condenser plate constituting avariable condenser, means for keeping said condenser charged, saidcondenser plate being so shaped, relatively, that the capacitance ofsaid condenser varies substantially sinusoidally as said rotor revolves,a phase indicating device, and means connecting said indicating deviceto said rotatable coil and said condenser, said rotatable coil and saidcondenser being adapted to generate alternating potentials Whose phaserelation is dependent upon the direction of said magnetic field withrespect to said reference line, whereby said indicating device is causedto register the angular relation of said magnetic field to saidreference line.

6. A device according to claim 3, said phase indicating devicecomprising a scale, a needle, a rotatable short-circuited conductingmember secured to said needle, and a field structure disposed adjacentto said short-circuited member and comprising a group of coils adaptedto be energized by one of said alternating potentials and a second groupof coils adapted to be energized by said other alternating potential,said field coils being so arranged and connected as to produce twooppositely rotating fields when energized.

7. A device according to claim 3, said phase indicating devicecomprising a scale, a needle, a rotatable vane secured to said needle,and a plurality of electrostatic field plates disposed adjacent to saidvane and adapted to be energized by one of said alternating potentialsto produce a rotating electrostatic field, said rotatable vane beingadapted to be energized by said other alternating potential.

8. In a device for indicating the angular relation of a magnetic fieldwith respect to a given reference line, means for generating twoalternating potentials of like frequency but differing in phase by anangle equal to the space angle between said field and said referenceline, a phase indicating device, and means connecting said generatingmeans and said phase indicating device, said phase indicating devicecomprising a scale, a needle, a rotatable short-circuited conductingmember secured to said needle, and a field structure disposed adjacentto said shortcircuited member and comprising a group of coils adapted tobe energized by one of said alternating potentials and a second group ofcoils adapted to be energized by said other alternating potential, saidfield coils being so arranged and connected as to produce two oppositelyrotating fields when energized.

9. In a device for; indicating the angular relation of a magnetic fieldwith respect to a given reference line, means for generating twoalternating potentials of like frequency but differing in phase by anangle equal to the space angle between said field and said referenceline, a phase indicating device, and means connecting said generatingmeans and said phase indicating device, said phase indicating devicecomprising a scale, a needle, a rotatable vane secured to said needle,and a plurality of electrostatic field plates disposed adjacent to saidvane and adapted to be energized by one of said alternating potentialsto produce a rotating electrostatic field, said rotatable vane beingadapted to be energized by said other alternating potential.

HENRY D. OAKLEY.

